1. Field of the Invention
The present invention relates to a liquid sample-spotting apparatus, and more particularly pertains to a liquid sample-spotting apparatus for use in spotting a given trace amount of a liquid sample on a sheet-form chemical analytical element for clinical tests by means of a micropipette. Further, the invention relates to a process for spotting a liquid sample on an analytical element using said apparatus.
2. Description of Prior Arts
Various body fluids are used as test solutions in clinical tests, and the most important test solution is blood. From the nature of the test solutions, it is important to use a small amount or a trace amount of a sample, and 5 .mu.l to 100 .mu.l of the solution is generally subjected to analysis. It will be understood that in measuring a trace amount of a sample an error in the amount of a solution to be measured relatively increases with a reduction in the amount to be measured.
However, when a sheet-form chemical analytical element having the outermost layer composed of a spreading layer capable of uniformly spreading the aqueous solution is used, it is evident that fluctuations in measured values caused by the valiability of the amount of the test sample to be measured are greatly reduced and measuring accuracy is remarkably improved as compared with solution methods which have been conventionally carried out. Accordingly, the sheet-form chemical analytical element is particularly suitable for use in the analysis of a trace amount of a sample. A micropipette is usually used for measuring such trace amount of sample solution.
In analytical operations using said sheet-form chemical analytical element, it has been found that measured results are affected by a spotting mode in depositing a small amount of the liquid solution in the form of a spot on the outermost layer composed of a porous membrane. More particularly, in spotting the liquid solution on the surface of the sheet-form chemical analytical element after taking a given amount of the liquid solution into a micropipette, the spreading conditions of the liquid solution in the porous membrane are influenced by the type of spotting operations, for example, a mode of dropping a liquid droplet on the membrane, a mode of directly depositing the sample on the membrane, and a mode of rubbing the sample against the membrane. Thus, fluctuations in the measured values increase.
Japanese Utility Model Provisional Publication No. 56(1981)-146241 discloses a liquid sample spotting apparatus which can keep the optimum operational conditions for spotting the liquid sample on the spreading layer of the sheet-form chemical analytical element with a manually operable micropipette and can reduce an operational error or an error due to an individual difference in order to minimize errors caused by the spotting conditions at the time of spotting the liquid sample. Since the liquid sample in this apparatus is caused to drop on the spreading layer of the sheet-form chemical analytical element, air bubbles may disadvantageously form within or on the surface of the liquid droplet supplied to said spreading layer so that the spreading conditions of the liquid sample within the spreading layer are adversely affected and fluctuations in the measured values increase.